The challenge to meet the ever-increasing demand for oil includes increasing crude oil recovery from heavy oil reservoirs. This challenge has resulted in expanding efforts to develop alternative cost efficient oil recovery processes (Kianipey, S. A. and Donaldson, E. C. 61st Annual Technical Conference and Exhibition, New Orleans, La., USA, Oct. 5-8, 1986). Heavy hydrocarbons in the form of petroleum deposits and oil reservoirs are distributed worldwide. These oil reserves are measured in the hundreds of billions of recoverable barrels. Because heavy crude oil has a relatively high viscosity, it is essentially immobile and cannot be easily recovered by conventional primary and secondary means.
Microbial Enhanced Oil Recovery (MEOR) is a methodology for increasing oil recovery by the action of microorganisms (Brown, L. R., Vadie, A. A., Stephen, O. J. SPE 59306, SPE/DOE Improved Oil Recovery Symposium, Oklahoma, 3-5 Apr., 2000). MEOR research and development is an ongoing effort directed to developing techniques to use microorganisms to modify crude oil properties to benefit oil recovery (Sunde. E., Beeder, J., Nilsen, R. K. Torsvik, T., SPE 24204, SPE/DOE 8th Symposium on enhanced Oil Recovery, Tulsa, Okla., USA, Apr. 22-24, 1992). In addition to MEOR activity, microbial treatment of underground formations can also be used to accelerate bioremediation processes for environmental clean up.
Microbial growth induced in the oil reservoir can lead to a number of changes in the reservoir chemistry resulting in improved oil recovery. These changes may include gas formation, acid formation, selective pore plugging, and alterations in partitioning of oil between petrologic and aqueous phases. MEOR processes are usually applied later in the life of oil recovery systems. When easily mobilized oil becomes depleted in the oil reservoir, water (injection water) is often injected into oil reservoirs to improve oil recovery. Injection water is also commonly used to introduce necessary components of a MEOR process into the reservoir. Because access to the reservoir is limited by the frequency and number of wells penetrating the underground formation, subterranean process control is often difficult. There is need therefore to control timing, location, and character of microbial activation in subterranean processes.
Controlled microbial growth allows better optimization of subterranean processes that are enhanced by microbial activity. For example, MEOR processes depend on microbial activity or the products of microbial activity to improve oil recovery in waterflooded oil formations. Furthermore, bioremediation of contaminated subsurface formations can be accelerated by inducing microbial activity. In situations illustrated by the examples below it is often desirable to target microbial activation to specific subsurface locations. This is often difficult because nutrients typically used to activate microbial activity in a targeted location may be consumed in transit by native microbial populations. Loss of nutrients in transit makes the overall process less efficient and more costly. In addition uncontrolled microbial growth can damage the subsurface formation, slowing subsurface water flow and increasing backpressure on the injection wells. In this disclosure, techniques to control activation of microbial growth upon injection into the subsurface formation to overcome the deficiencies described above are disclosed.